1. Field of the Invention
The present invention relates to a polishing apparatus and a polishing method, and more particularly to a polishing apparatus and a polishing method for polishing a surface conductive film (metal film) of a substrate, such as a semiconductor wafer, and flattening the surface of the substrate.
2. Description of the Related Art
For the formation of interconnects in a semiconductor device, a so-called damascene process is employed which comprises forming a barrier metal film on interior surfaces of trenches and contact holes formed in an insulating film, filling a metal such as copper, as an interconnect and contact material, into the trenches and contact holes, and then removing an extra metal by chemical mechanical polishing (CMP). A damascene process, when it forms interconnects and contacts simultaneously, is called dual damascene process.
FIG. 1A to 1C illustrate an exemplary dual damascene process for forming copper interconnects. First, as shown in FIG. 1A, an insulating film 2 of, e.g., an SiO2 oxide film or a low-k material is deposited on a conductive layer 1a, in which semiconductor elements are formed, on a semiconductor base 1 of a substrate W; via holes 3 and trenches 4 are formed in the insulating film 2 by the lithography/etching technique; and a barrier metal film (barrier layer) 5 of TaN or the like is formed on the entire surface of the substrate and a seed layer 7, which serves as a feeding layer during electroplating, is formed on the barrier layer 5.
Subsequently, as shown in FIG. 1B, copper plating is carried out on the surface of the substrate W to deposit a copper film 6 on the insulating film 2 while filling copper into the via holes 3 and the trenches 4. Thereafter, the copper film 6, the seed layer 7 and the barrier metal layer 5 on the insulating film 2 are removed by chemical mechanical polishing (CMP) to make the surface of the copper film 6, embedded in the via holes 3 and the trenches 4, approximately flush with the surface of the insulating film 2, thereby forming interconnects (copper interconnects) composed of the copper film 6 in the insulating film, as shown in FIG. 1C.
A polishing apparatus, which polishes and removes an extra conductive film (metal film), such as copper, from a substrate surface, includes a polishing table having a polishing surface, generally constituted by a polishing pad, and a top ring for holding a substrate (workpiece). In operation, while pressing a surface conductive film of a substrate, held by the top ring, against the polishing surface of the polishing table at a predetermined pressure, the polishing table and the top ring are moved relative to each other and, at the same time, a polishing liquid containing abrasive grains, such as silica (SiO2), is supplied onto the polishing surface of the polishing table, thereby polishing the surface of the conductive film into a flat mirror surface.